I'm just starting a project to build a universal Engineer's Remote Control Unit [EG. able to send the Panasonic 0xF2 code, etc.].
I have seen that IR LEDs come with (at least) three distinctly different coloured lenses, namely "Crystal Clear", "Blue" and "Black" ...Using Google, I can find no information about the difference made by the colour of the lens.
So my question is: Why do Infrared LEDs come with different coloured lenses?